tranquillity vs composure

tranquillity and composure both are nouns.

Word	Noun	Adjective	Verb	Adverb
tranquillity	Yes	No	No	No
composure	Yes	No	No	No

As nouns, composure is a hypernym of tranquillity; that is, composure is a word with a broader meaning than tranquillity:

Other hypernyms of tranquillity include calm, calmness, equanimity.

tranquillity (noun)	composure (noun)
a disposition free from stress or emotion	steadiness of mind under stress
a state of peace and quiet
an untroubled state; free from disturbances